This invention relates generally to a method and apparatus for sequentially working on a sheet with first one side up and then the other using a pair of work units while the same edge of the sheet leads as the sheet passes through each of the work units. The particular application for which the invention is intended, involves printing equipment for printing on both sides of a sheet, and the following description is expressed primarily in terms of that environment. It will however be readily apparent that sheet handling equipment of this nature will be equally applicable in other situations.
There are known printing systems which are effective to simultaneously print on opposite sides of a sheet. These known printing systems are rather complicated in their mode of operation. Somewhat simplier printing systems have been used which are effective to print on only one side of a sheet. Still other printing systems have utilized a pair of printing units to sequentially print on opposite sides of a sheet.
Some of the known printing units which sequentially print on opposite sides of a sheet have utilized inverters to invert the sheet between the printing units. When these known inverters are utilized to invert a sheet, a first edge of the sheet leads as it passes through the first printing unit and the second edge of the sheet leads as it passes through the second printing unit. Some of these known inverters have utilized cylinders which have relatively complicated gripper arrangements to effect a turning over or inverting of the sheet.